Encoding system for forming two-channel signals from a plurality of sound signals

ABSTRACT

In an encoding system in which front-left and right audio input signals are coupled to left and right channels with a reference phase-shift angle, and back-left and right audio input signals are coupled to the left channel with the reference phase-shift angle plus 90* and to the right channel with the reference phaseshift angle minus 90*, a left-center audio input signal is coupled in a large proportion to the left channel with the reference phase-shift angle and in a small proportion to the right channel with the reference phase-shift angle minus 90* and a right-center signal is coupled in a large proportion to the right channel with the reference phase-shift angle and in a small proportion to the left channel with the reference phase-shift angle plus 90*.

United States Patent Takahashi [4 1 Oct. 29, 1974 ENCODING SYSTEM FORFORMING Susumu Takahashi, Tokyo, Japan Assignee: Sansui Electric Co.,Tokyo, Japan Filed: Nov. 9, 1973 Appl. No.: 414,512

[30] Foreign Application Priority Data Dec. 29, 1972 Japan 47-2774References Cited UNITED STATES PATENTS 7/1973 Baver l79/l00.4 ST l2/l973Takahashi l/l974 ltoh l79/100.4 ST

OTHER PUBLICATIONS Proposed Universal Encoding Standards forCompatil79/l0O.4 ST

ble Four-Channel Matrixing, by ltoh, Journal AES-A- pril 1972.

Primary Examiner-Kathleen H. Claffy Assistant Examiner-Thomas DAmicoAttorney, Agent, or FirmHarris, Kern, Wallen & Tinsley [57] ABSTRACT Inan encoding system in which front-left and right audio input signals arecoupled to left and right channels with a reference phase-shift angle,and back-left and right audio input signals are coupled to the leftchannel with the reference phase-shift angle plus 90 and to the rightchannel with the reference phase-shift angle minus 90, a left-centeraudio input signal is coupled in a large proportion to the left channelwith the reference phase-shift angle and in a small proportion to theright channel with the reference phase-shift angle minus 90 and aright-center signal is coupled in a large proportion to the rightchannel with the reference phase-shift angle and in a small proportionto the left channel with the reference phase-shift angle plus 90.

6 Claims, 2 Drawing Figures PHASE SHIFTER 22 ENCODING SYSTEM FOR FORMINGTWO-CHANNEL SIGNALS FROM A PLURALITY or SOUND SIGNALS This inventionrelates to a four-channel matrix encoding system for forming two-channelsignals from a plurality of sound signals.

Already known is an encoding system which couples a left-front signal(LF) and a right-front signal (RF) in large and small proportionsrespectively to the left channel L with a reference phase shift amount;couples the RF signal and the LF signal in large and small proportionsrespectively to the right channel R with the reference phase shiftamount; couples a left-back signal (LB) and a right-back signal (RB) inlarge and small proportions respectively to the left channel L with thereference phase shift amount plus 90; and couples the RB signal and theLB signal in large and small proportion respectively to the rightchannel R with the reference phase shift amount minus 90.

Signals of the left and right channels L and R generated by the priorart encoding system arranged as described above may be expressed by thefollowing equation:

R=RF+ALFjRBjALB (n where A denotes a matrix coefficient whose typicalvalue is 0.414.

To attain the most distinct separation of left and right signalsobtained on the reproduction side, the customary practice is to couple aleft-center signal LC and right-center signal RC to the left and rightchannels L and R respectively with the reference phase shift amount.

Where the two-channel signals L and R shown in the above equation (1)are reproduced into four-channel signals by the known decoder,separation between two adjacent channels is 3db. Separation betweendiagonally opposite channels is To improve such indistinct separation ofchannels on the reproduction side, there has already been proposed aseparation enhancing decoder for momentarily changing the mixing ratioof two-channel signals or a matrix coefficient according to thecondition of the two-channel signals. For details of the decoder, referto the copending US. Pat. application Ser. No. 298,933, filed on Oct.19, 1972, with the title DECODER FOR USE IN 4-2-4 MATRIX PLAYBACKSYSTEM.

The decoder is provided with a control unit for detecting the levelrelationship of front and back signals and generating a first and asecond control output.

The equation (1) above shows that where the back signals LB and RB havea negligible amplitude as compared with that of the front signals LF andRF the twochannel signals are substantially in phase, and thatconversely where the front signals LF and RF have a negligible amplitudeas compared with that of the back signals LB and RR, the two-channelsignals are substantially 180 out of phase. In case of LF RF LB RB, thetwo-channel signals are 90 out of phase.

Where the two-channel signals L and R are in phase, the first controloutput takes a positive maximum value with respect to the referentialvoltage level whereas the second control output assumes a negativemaximum value, or vice versa where the two-channel signals L and R are180 out of phase. Where the two-channel signals L and R are out ofphase, the first and second control outputs have a voltage level equalto the referential voltage level.

Where the two-channel signals L and R have the same phase, one type ofprior art decoder enhances separation between front-left and rightreproduced signals, but reduces separation between back-left and rightreproduced signals and also increases the voltage level of the frontsignals and decreases that of the back signals, thereby promotingseparation between the front and back reproduced signals. Where thetwochannel signals L and R are out of phase, the prior art decodercarries out an opposite operation to that mentioned above. Where thetwo-channel signals L and R are 90 out of phase, the decoder is operatedin the same manner as the other conventional decoders without changingthe matrix coefficients.

Where a decoder carrying out the above-mentioned operation is suppliedwith, for example, a right signal R and a left signal L including aleft-center signal LC, the control unit does not act on the left-centersignal LC. Therefore, this signal LC is reproduced by the leftfrontloudspeaker and left-back loudspeaker with an equal level. Since,however, two-channel signals are supplied to the decoder generally afterbeing reproduced through a pickup cartridge from a phonographic record,it is difficult to prevent the left-center signal from necessarilyappearing in the right signal R as a crosstalk component. In this case,it is also difficult to determine whether the crosstalk component hasthe same or opposite phase with respect to the original signal or theleft-center signal. In either case, existence of the left-center signalcauses the decoder to take the erroneous action of controlling the frontand back signals.

It is accordingly an object of this invention to provide an encodingsystem capable of preventing two-channel signals reproduced through arecording medium from presenting the same or opposite phase relative tothe left or right-center signal.

Another object of the invention is to provide an ,encoding systemcapable of producing two-channel signals in the form adapted for adecoder to reproduce separation enhanced output signals.

According to an aspect to this invention, there is provided an encodingsystem in which at least first to fourth sound signals desired to becoupled mainly to first to fourth loudspeakers surrounding a listenerare utilized in forming first and second channel signals, and first andsecond sound signals are coupled to the first channel in large and smallproportions respectively with a reference phase shift amount, second andfirst sound signals are coupled to the second channel in large and smallproportions respectively with the reference phase shift amount, thirdand fourth sound signals are coupled to the first channel in large andsmall proportions respectively with a phase shift amount of thereference phase shift amount plus 90, and the fourth and third soundsignals are coupled to the second channel in large and small proportionswith a phase shift amount of the reference phase shift amount minus 90,the improvement comprising means for coupling a fifth sound signaldesired to have its sound image localized between the first and thirdloudspeakers to the first channel in a large proportion with thereference phase shift amount; means for coupling the fifth sound signalto the second channel in a small proportion with a phase shift amounthaving substantially 90 phase difference with respect to the referencephase shift amount; means for coupling a sixth sound signal desired tohave its sound image localized between the second and fourthloudspeakers to the second channel in a large proportion with thereference phase shift amount; and means for coupling the sixth soundsignal to the first channel in a small proportion with a phase shiftamount having substantially 90 phase difference with respect to thereference phase shift amount.

This invention can be more fully understood from the following detaileddescription when taken in conjunction with the accompanying drawing, inwhich:

FIG. 1 is a circuit diagram of an encoding system according to oneembodiment of this invention; and

FIG. 2 is vector diagrams given for better understanding of theinvention.

Referring to FIG. 1 reference numerals 11 to 14 denote input terminalssupplied with LF, LB, RB and RF audio input signals respectively. Theseinput terminals are connected to a resistance matrix circuit 15containing resistors 16 to 21. A sum output of an LF signal having alarge proportion and an RF signal having a small proportion is drawn outfrom the junction of the resistor 16 and blend resistor 20. This outputis coupled to a first phase shifter 22. Further, a sum output of an RFsignal having a large proportion and an LF signal having a smallproportion is delivered from the junction of the resistor 19 and blendresistor 20. This output is coupled to a second phase shifter 23. A sumoutput of an LB signal having a large proportion and an RB signal havinga small proportion is obtained from the junction of the resistor 17 andblend resistor 21. This output is coupled to a third phase shifter 24.Further, a sum output of an RB signal having a large proportion and anLB signal having a small proportion is taken out of the junction of theresistor 18 and blend resistor 21. This output is coupled to a fourthphase shifter 25.

Output signals from the first and third phase shifters 22 and 24 arecoupled to an output terminal 26 through an adder 27 to produce aleft-channel signal L. Output signals from the second and fourth phaseshifters 23 and 25 are coupled to an output terminal 28 through an adder29 to produce a right-channel signal R.

The first and second phase shifters 22 and 23 have substantially thesame phase-shifting characteristic over entire audible frequency range,so as to shift the phase of input signal thereto by an reference angle4). On the other hand, the third phase shifter 24 has a phase-shiftingcharacteristic so as to shift the phase of input signal thereto by thereference angle 11) plus 90 and the fourth phase shifter has a phaseshifting charactcristic so as to the phase of input signals by thereference angle 4) minus 90. Accordingly, left and right channel signalsL and R obtained at the output terminals 26 and 28 can obviously beindicated by the afore mentioned equation (1).

Reference numerals 30 and 31 show input terminals supplied with aleft-center signal LC and a right-center signal RC respectively. The LCsignal is coupled to the first phase shifter 22 in a large proportionand to the fourth phase shifter 25 through a resistor 32 in a smallportion. The RC signal is coupled to the second phase shifter 23 in alarge proportion and to the third phase shifter 24 through a resistor 33in a small portion.

The resistors constituting the resistor matrix circuit 15 are chosen tohave such resistance values as to cause the ratio of the smallproportion to the large proportion of the LF, LB, RB and RF to indicatea value of 0.414. On the other hand, the small and large proportions ofthe LC and RC signals may be so chosen as to have a ratio of, forexample, 0.01 to 0.1 (or 40 db to 20db).

There will now be described the appearance of a crosstalk. If, in casetwo-channel signals R and L are reproduced from a phonographic disk, therightchannel signal R contains a right-center signal RCO, then thereproduced left-channel signal L will be contaminated by a crosstalkcomponent ARCl (about 30db) having the same phase as that of the RC0signal or another crosstalk component ARC2 having an opposite phase fromthat of the RC0 signal. Further, the left signal L is contaminated by athird crosstalk component ARC3 (about 20db) which was carried into theleft signal L on the encoder side in quadrature with the RC0 signal. Asthe result, the reproduced left-channel signal L contains a resultantcrosstalk component ARC4 formed of crosstalk components ARC3 and ARCl ora resultant crosstalk component ARCS formed of crosstalk components ARC3and ARCZ. Since the crosstalk component ARCl or ARC2 has a smallerproportion than the crosstalk component ARC3, the resultant crosstalkARC4 or ARCS is approximately in quadrature with the aforesaid RCOcomponent. Accordingly, the reproduced two-channels L and R are inquadrature with each other with respect to the left-center signal LC orright-center signal RC. Where, therefor, such two-channel signals aresupplied to the previously described separation enhancing decoder, thenthe existence of the LC or RC signal can substantially prevent the frontand back signals from being controlled by mistake.

Though, in FIG. 1, the left-center signal LC and the right-center signalRC of a small proportion are coupled to the right and left channels withphase-shifts of 90 and d respectively, the left-center signal LC of asmall proportion may be coupled to the right channel with a phase-shiftof +90 and the rightcenter signal RC to the left channel with aphase-shift of 90.

What is claimed is:

1. An encoding system in which at least first to fourth sound signalsdesired to be coupled mainly to first to fourth loudspeakers surroundinga listener are utilized in forming first and second channel signals, andfirst and second sound signals are coupled to the first channel in largeand small proportions respectively with a reference phase shift amount,second and first sound signals are coupled to the second channel inlarge and small proportions respectively with the reference phase shiftamount, third and fourth sound signals are coupled to the firstchannelin large and small proportions respectively with a phase shiftamount of the reference phase shift amount plus 90, and the fourthandthird sound signals are coupled to the second channel in large andsmall proportions with a phase shift amount of the reference phase shiftamount minus 90, the improvement comprising means for coupling a fifthsound signal desired to have its sound image localized between saidfirst and third loudspeakers to the first channel in a large proportionwith the reference phase shift amount; means for coupling said fifthsound signal to the second channel in a small proportion with a phaseshift amount having substantially 90 phase difference with respect tothe reference phase shift amount; means for coupling a sixth soundsignal desired to have its sound image localized between the second andfourth loudspeakers to the second channel in a large proportion with thereference phase shift amount; and means for coupling said sixth soundsignal to the first channel in a small proportion with a phase shiftamount having substantially 90 phase difference with respect to thereference phase shift amount.

2. An encoding system for encoding at least first to fourth soundsignals desired to be coupled mainly to first to fourth loudspeakerssurrounding a listener into first and second channel signals, comprisingfirst means for mixing the first sound signal in a large proportion andthe second sound signal in a small proportion; second means for mixingthe second sound signal in a large proportion and the first sound signalin a small proportion; third means for mixing the third sound signal ina large proportion and a fourth sound signal in a small proportion;fourth means for mixing the fourth sound signal in a large proportionand the third sound signal in a small proportion; a first phase shiftercoupled to the output of said first means; a second phase shiftercoupled to the output of said second means and having substantially thesame phase shifting characteristic as said first phase shifter over theentire audible frequency range; a third phase shifter coupled to theoutput of said third means and having a phase shifting characteristic ofplus 90 difference with respect to those of said first and second phaseshifters; a fourth phase shifter coupled to the output of said fourthmeans and having a phase shifting characteristic of minus 90 differencewith respect to those of said first and second phase shifters; means forcoupling a fifth sound signal desired to have its sound image localizedbetween the first and third loudspeakers to the input of said firstphase shifter in a large proportion; means for coupling said fifth soundsignal to the input of said fourth phase shifter in a small proportion;means for coupling a sixth sound signal desired to have its sound imagelocalized between the second and fourth loudspeakers to the input ofsaid second phase shifter in a large proportion; means for coupling saidsixth sound signal to the input of said third phase shifter in a smallproportion; means for mixing output signals from said first and thirdphase shifters; and means for mixing output signals from said second andfourth phase shifters.

3. An encoding system for coupling to the firstand second channels firstto fourth sound signals desired to be coupled mainly to first to fourthloudspeakers surrounding a listener comprising: means for coupling thefirst and second sound signal to the first channel in large and smallproportions respectively with a reference phase shift amount; means forcoupling the second and first sound signals to the second channel inlarge and small proportions respectively with the reference phase shiftamount; means for coupling the third and fourth sound signals to thefirst channel in large and small proportions respectively with thereference phase shift amount plus 90; means for coupling the fourth andthird sound signals to the second channel in large and small proportionswith the reference phase shift amount minus 90; means for coupling afifth sound signal desired to have its sound image localized between thefirst and third loudspeakers to the first channel in a large proportionwith the reference phase shift amount; means for coupling the fifthsound signal to the second channel in a small proportion with a phaseshift amount having substantially phase difference with respect to thereference phase shift amount; means for coupling a sixth sound signaldesired to have its sound image localized between the second and fourthloudspeakers to the second channel in a large proportion with thereference phase shift amount; and means for coupling the sixth soundsignal to the first channel in a small proportion with a phase shiftamount having substantially 90 phase difference with respect to thereference phase shift amount.

4. An encoding system according to claim 3 wherein the small proportionof the first to fourth sound signals bears a ratio of about 0.414 to thelarge proportion thereof.

5. An encoding system according to claim 3 wherein the small proportionof the fifth and sixth sound signals bears a ratio of 0.01 to 0.1 to thelarge proportion thereof.

6. An encoding system for encoding first to fourth sound signals desiredto be coupled mainly to first to fourth loudspeakers surrounding alistener into first and second channel signals comprising: first tofourth input terminals adapted to receive the first to fourth soundsignals respectively; a fifth input terminal adapted to receive a fifthsound signal desired to have its sound image localized between the firstand third loudspeakers; a sixth input terminal adapted to receive asixth sound signal desired to have its sound image localized between thesecond and fourth loudspeakers; first and second output terminals;matrix means connected to said first to fourth input terminals so as toform first, second, third and fourth output signals, said first outputsignal being a sum of the first sound signal having a large amplitudeand the second sound signal having a small amplitude, said second outputsignal being a sum of the first sound signal having a small amplitudeand the second sound signal having a large amplitude, said third outputsignal being a sum of the third sound signal having a large amplitudeand the fourth sound signal having a small amplitude, and said fourthoutput signal being a sum of the third sound signal having a smallamplitude and the fourth sound signal having a large amplitude; a firstphase shifter connected to receive said first output signal and having areference phase shifting characteristic; a second phase shifterconnected to receive said second output signal and having the referencephase shifting characteristic; a third phase shifter connected toreceive said third output signal and having a phase shiftingcharacteristic of plus 90 difference with respect to the reference phaseshifting characteristic; a fourth phase shifter connected to receivesaid fourth output signal and having a phase shifting characteristic ofminus 90 difference with respect to the reference phase shiftingcharacteristic; means for coupling output signals from said first andthird phase shifters to said first output terminal; means for couplingoutput signals from said second and third phase shifters to said secondoutput terminal; means for coupling a fifth sound signal to said firstphase shifter with a large amplitude; means for coupling the fifth soundsignal to said third phase shifter with a small amplitude; means forcoupling a sixth sound signal to said second phase shifter with a largeamplitude; and means for coupling the sixth sound signal to said fourthphase shifter with a small amplitude.

1. An encoding system in which at least first to fourth sound signalsdesired to be coupled mainly to first to fourth loudspeakers surroundinga listener are utilized in forming first and second channel signals, andfirst and second sound signals are coupled to the first channel in largeand small proportions respectively with a reference phase shift amount,second and first sound signals are coupled to the second channel inlarge and small proportions respectively with the reference phase shiftamount, third and fourth sound signals are coupled to the first channelin large and small proportions respectively with a phase shift amount ofthe reference phase shift amount plus 90*, and the fourth and thirdsound signals are coupled to the second channel in large and smallproportions with a phase shift amount of the reference phase shiftamount minus 90*, the improvement comprising means for coupling a fifthsound signal desired to have its sound image localized between saidfirst and third loudspeakers to the first channel in a large proportionwith the reference phase shift amount; means for coupling said fifthsound signal to the second channel in a small proportion with a phaseshift amount having substantially 90* phase difference with respect tothe reference phase shift amount; means for coupling a sixth soundsignal desired to have its sound image localized between the second andfourth loudspeakers to the second channel in a large proportion with thereference phase shift amount; and means for coupling said sixth soundsignal to the first channel in a small proportion with a phase shiftamount having substantially 90* phase difference with respect to thereference phase shift amount.
 2. An encoding system for encoding atleast first to fourth sound signals desired to be coupled mainly tofirst to fourth loudspeakers surrounding a listener into first andsecond channel signals, comprising first means for mixing the firstsound signal in a large proportion and the second sound signal in asmall proportion; second means for mixing the second sound signal in alarge proportion and the first sound signal in a small proportion; thirdmeans for mixing the third sound signal in a large proportion and afourth sound signal in a small proportion; fourth means for mixing thefourth sound signal in a large proportion and the third sound signal ina small proportion; a first phase shifter coupled to the output of saidfirst means; a second phase shifter coupled to the output of said secondmeans and having substantially the same phase shifting characteristic assaid first phase shifter over the entire audible frequency range; athird phase shifter coupled to the output of said third means and havinga phase shifting characteristic of plus 90* difference with respect tothose of said first and second phase shifters; a fourth phase shiftercoupled to the output of said fourth means and having a phase shiftingcharacteristic of minus 90* difference with respect to those of saidfirst and second phase shifters; means for coupling a fifth sound signaldesired to have its sound image localized between the first and thirdloudspeakers to the input of said first phase shifter in a largeproportion; means for coupling said fifth sound signal to the input ofsaid fourth phase shifter in a small proportion; means for coupling asixth sound signal desired to have its sound image localized between thesecond and fourth loudspeakers to the input of said second phase shifterin a large proportion; means for coupling said sixth sound signal to theinput of said third phase shifter in a small proportion; means formixing output signals from said first and third phase shifters; andmeans for mixing output signals from said second and fourth phaseshifters.
 3. An encoding system for coupling to the first and secondchannels first to fourth sound signals desired to be coupled mainly tofirst to fourth loudspeakers surrounding a listener comprising: meansfor coupling the first and second sound signal to the first channel inlarge and small proportions respectively with a reference phase shiftamount; means for coupling the second and first sound signals to thesecond channel in large and small proportions respectively with thereference phase shift amount; means for coupling the third and fourthsound signals to the first channel in large and small proportionsrespectively with the reference phase shift amount plus 90*; means forcoupling the fourth and third sound signals to the second channel inlarge and small proportions with the reference phase shift amount minus90*; means for coupling a fifth sound signal desired to have its soundimage localized between the first and third loudspeakers to the firstchannel in a large proportion with the reference phase shift amount;means for coupling the fifth sound signal to the second channel in asmall proportion with a phase shift amount having substantially 90*phase difference with respect to the reference phase shift amount; meansfor coupling a sixth sound signal desired to have its sound imagelocalized between the second and fourth loudspeakers to the secondchannel in a large proportion with the reference phase shift amount; andmeans for coupling the sixth sound signal to the first channel in asmall proportion with a phase shift amount having substantially 90*phase difference with respect to the reference phase shift amount.
 4. Anencoding system according to claim 3 wherein the small proportion of thefirst to fourth sound signals bears a ratio of about 0.414 to the largeproportion thereof.
 5. An encoding system according to claim 3 whereinthe small proportion of the fifth and sixth sound signals bears a ratioof 0.01 to 0.1 to the large proportion thereof.
 6. An encoding systemfor encoding first to fourth sound signals desired to be coupled mainlyto first to fourth loudspeakers surrounding a listener into first andsecond channel signals comprising: first to fourth input terminalsadapted to receive the first to fourth sound signals respectively; afifth input terminal adapted to receive a fifth sound signal desired tohave its sound image localized between the first and third loudspeakers;a sixth input terminal adapted to receive a sixth sound signal desiredto have its sound image localized between the second and fourthloudspeakers; first and second output terminals; matrix means connectedto said first to fourth input terminals so as to form first, second,third and fourth output signals, said first output signal being a sum ofthe first sound signal having a large amplitude and the second soundsignal having a small amplitude, said second output signal being a sumof the first sound signal having a small amplitude and the second soundsignal having a large amplitude, said third output signal being a sum ofthe third sound signal having a large amplitude and the fourth soundsignal having a small amplitude, and said fourth output signal being asum of the third sound signal having a small amplitude and the fourthsound signal having a large amplitude; a first phase shifter connectedto receive said first output signal and having a reference phaseshifting characteristic; a second phase shifter connected to receivesaid second output signal and having the reference phase shiftingcharacteristic; a third phase shifter connected to receive said thirdoutput signal and having a phase shifting characteristic of plus 90*difference with respect to the reference phase shifting characteristic;a fourth phase shifter connected to receive said fourth output signaland having a phase shifting characteristic of minus 90* difference withrespect to the reference phase shifting characteristic; means forcoupling output signals from said first and third phase shifters to saidfirst output terminal; means for coupling output signals from saidsecond and third phase shifters to said second output terminal; meansfor coupling a fifth sound signal to said first phase shifter with alarge amplitude; means for coupling the fifth sound signal to said thirdphase shifter with a small amplitude; means for coupling a sixth soundsignal to said second phase shifter with a large amplitude; and meansfor coupling the sixth sound signal to said fourth phase shifter with asmall amplitude.